1. Field of the Invention
The present invention relates to disinfectant compositions, and, more particularly, to a chlorine dioxide disinfectant composition, methods of use, and methods of making.
2. Description of Related Art
Many disinfectant compositions have been known in the art, most with some degree of undesirable side effects. For example, chlorine is an inexpensive and effective disinfectant; however, being highly reactive, chlorine generates precursors of carcinogens and disinfection byproducts. Chlorine is also a powerful bleach, is highly toxic, and is largely ineffective in disinfecting gram-positive bacteria. Chlorine's functions, in order of strength, include chlorination, oxidation, bleaching, and disinfection.
Ozone is primarily an oxidizer having limited disinfection capabilities in microbially contaminated water owing to its low solubility. Ultraviolet light (uv) is not effective in treating water that is microbially or biologically contaminated. Hydrogen peroxide, while being highly soluble in water, is not practical for use in water treatment. Bleach, although an effective bleaching and oxidizing agent, is highly reactive and is known to generate undesirable byproducts.
Chlorine dioxide does not possess any of the above-mentioned drawbacks, and is believed especially effective in water and wastewater treatment, and in aqueous solutions. Chlorine dioxide does not incur environmental problems or health concerns, and does not generate disinfection byproducts (DBPs), except for a small amount of chlorite ion (ClO2−) as an intermediate that spontaneously decomposes into harmless products, chloride ion (Cl−) and oxygen. Further, chlorine dioxide does not create chlorinated organics, including precursor materials of trihalomethanes (THMs), unlike chlorine.
Chlorine dioxide is approximately five times more soluble than chlorine in water and direct exposure to the gas is much less harmful than to chlorine at similar concentrations. In addition, chlorine dioxide is very effective in disinfecting gram-positive bacteria, which cannot be treated effectively by other known disinfectants.
If used properly in its pure form, chlorine dioxide can produce residuals at an exit stream of a treatment system similar to those of chlorine, and is effective in reducing turbidity, discoloring, and deodorizing.
Chlorine dioxide made by prior art methods is known to be contaminated with free available chlorine (FAC), chlorite ion, chlorate ion, chloride ion, and hypochlorite ion, arising from process raw materials, process intermediates, and synthesis byproducts. Even if the contaminant concentrations are low, they may affect subsequent disinfection chemistry, as well as the stability of the chlorine dioxide product via a variety of chemical reactions, including oxidation-reduction reactions, as well as autocatalytic reactions. Some of these reactions include, but are not intended to be limited to:Cl2+H2OHClO+HClHClOH++ClO−ClO2+ClO−+e−2Cl−+3/2O2 ClO2+ClO2−+e−2Cl−+2O2 ClO2+e−Cl−+O2 ClO3−ClO2−+(O)ClO2+(O)Cl−+ 3/2O2 The presence of other oxychloro compounds in the chlorine dioxide aqueous solution can lead to many other chemical reactions that are undesirable for the intended objects of the product. Such reactions not only create harmful byproducts, but also can cause the premature decomposition of the product chlorine dioxide.
Chlorine dioxide is not stable as a product gas, being susceptible to uv and to self-decomposition into chlorine and oxygen. Therefore, chlorine dioxide has typically been in aqueous solution, limiting its applications.
Even in aqueous solution chlorine dioxide is unstable, further limiting its use as a liquid product. Owing to its instability, chlorine dioxide has never been approved as a transportation chemical by the U.S. Department of Transportation or the United Nations. Thus on-site generation has been the only means for utilizing chlorine dioxide, which must be used within a day or two at most, 80-90% of its strength typically lost within 24 hours. The decomposition mechanisms have not until now been understood.
Decomposition of chlorine dioxide may be attributed to six possible causes:
1. Chlorine dioxide exhibits vapor-phase (or dry-phase) decomposition.
2. Gas-phase decomposition of chlorine dioxide is promoted in the presence of air, specifically, oxygen. In aqueous solution, the dissolved oxygen concentration being only ˜9.2 mg/L, decomposition is less.
3. Decomposition in both the dry and wet phases is also promoted in the presence of other strong oxidants and reducing agents. Although chlorine dioxide is generally an oxidant, it can function as a reducing agent when in contact with a stronger oxidizer. Therefore, any impurities in the product stream or solution would participate in a chemical reaction, including decomposition of chlorine dioxide. Once decomposition begins, the decomposition products, including oxygen, act to promote further decomposition reactions. Such an accelerated reaction is termed “autocatalytic,” meaning that the undesirable reactions are self-sustaining, eventually leading to substantially complete decomposition of the chlorine dioxide in the system.
4. Chlorine dioxide decomposition is promoted by uv irradiation, since the molecules readily absorb radiation.
5. Chlorine dioxide decomposition is very strongly promoted by mechanical agitation or shock, which can be compounded by oxygen-triggered decomposition as described in (2) above, since mechanical agitation can create air pockets and increase the concentration of dissolved oxygen in the water.
6. Chlorine dioxide decomposition is greater in a container having a large headspace, driven by the vapor pressure of chlorine dioxide, promoting movement from the aqueous phase to the vapor phase.
Pure chlorine dioxide is known to be produced by the system and method of commonly owned U.S. Pat. Nos. 5,855,861 and 6,051,135, the contents of which are incorporated herein by reference. There are, however, no known systems, compositions, or methods for achieving long-term storage and preservation of pure chlorine dioxide, which would be desirable.